1. Field of the Invention
The present invention relates to a toner and a developer using the toner for use in electrophotographic image forming processes in copiers facsimiles, printers, etc., and to an image developer and an image forming apparatus using the developer.
2. Discussion of the Background
Recently, toners for use in electrophotographic image forming processes are having smaller particle diameters and ensphered to comply with increasing demands for higher quality images. When a toner has a smaller particle diameter, the toner has better reproducibility of a dot. When ensphered, the toner has better developability and transferability. Since conventional kneading and pulverizing methods of preparing a toner have much difficulty in preparing such an ensphered toner having a smaller particle diameter, polymerized toners prepared by a suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method or the like method are being used.
However, the polymerized toners still have some problems to be solved. The polymerized toners are studied from various aspects to have better powder fluidity and transferability by reducing a particle diameter thereof and being ensphered, and have good thermostable preservability, low-temperature fixability and hot offset resistance. For example, Japanese Laid-Open Patent Publication No. 11-149180 discloses a method of dispersing toner constituents including a prepolymer including an isocyanate group in an aqueous medium, and adding amines thereto such that a cross-linking reaction and/or an elongation reaction of the prepolymer are performed to prepare a toner. Such a reaction can prepare a toner having a polymer outer shell, which can improve thermostable preservability of the toner.
In the above-mentioned method, depending on volume ratios of materials included in the toner constituents, performances of the reactions in the aqueous medium differ, resulting in preparation of a toner not having a desired particle diameter or a toner not having desired chargeability. Particularly when the toner constituents include the amines as above, the resultant toner tends to be positively charged. Therefore, an influence on chargeability of a toner of such positively charging constituents needs to be considered to prepare a toner to be negatively charged, which is used in negatively charging reverse developing methods.
Because of these reasons, a need exists for a stable negatively-charged toner having a small particle diameter distribution, good developability, transferability, low-temperature fixability, hot offset resistance and thermostable preservability.